Research Division Seminar
Weighting the Giants: The Study of Cored Early-Type Galaxies and Their Supermassive Black Holes

Abstract

The most massive elliptical galaxies are known to exhibit a central deficit of stars. These depleted "cores" are believed to form through dry mergers between early-type galaxies (ETGs) via a process called core scouring. In this process, stars are ejected from the center due to interactions with the merging black holes of the gas-poor progenitor galaxies. This phenomenon leaves a distinct imprint on the stellar distribution, making it a valuable tracer for investigating the formation history of ETGs.

To study this effect, a dynamical model is required that can recover the intrinsic orbit structure and mass distribution of the galaxy under study. We developed a novel, state-of-the-art dynamical Schwarzschild modeling technique, capable of recovering the intrinsic structure of even triaxial systems with an unprecedented precision.

Applying this model to high-resolution MUSE spectral data of the massive core elliptical galaxy NGC 5419, we identified an ideal candidate to investigate the dry-merging scenario of ETGs in greater detail. NGC 5419 has a well-depleted core, yet HST data reveal a double nucleus, suggesting that two supermassive black holes (SMBHs) from the progenitor galaxies have not yet completely merged.

We find that NGC 5419 is observed in an intermediate stage of core evolution, hosting an as-yet-unmerged SMBH binary system. NGC 5419 is the first galaxy observed in this transitional state, providing previously unobserved insights into the formation mechanism of ETGs.

Our dynamical models of NGC 5419 reveal a total SMBH mass of Mbh = (1.0 ± 0.08) × 10^10 Msol, establishing NGC5419 as host to one of the most massive BHs discovered in the local universe so far.